'I'm really not computer smart ...' - turning ON the MacBook; connecting to the internet; locating, registering, and posting to 'macosx.com' shows you are quite 'computer smart'.
'... and pretty new to a Mac.' - welcome to the Macintosh community, and macosx.com.
'... my desktop is frozen, as is Finder' - 'Finder' maintains the 'Desktop', so a frozen 'Finder' will inhibit your access to the 'Desktop'.
'... but all my other applications are working fine.' - if your currently launched applications continue to work, and can be clicked on - to be brought forward, yet 'Finder' remains 'frozen' or occupied, 'and' you cannot launch (open, run) any additional applications - you have experienced / are experiencing a low level system failure.
Yes, 'Finder' itself can bring such a failure about - and Apple has yet to release a fix for such.
'Finder' itself is Apples one failure to properly port to MacOS X from its world class predecessor - 'System 9.2.2' (and earlier).
'Finder', like 'Safari', is known to generate excessive number of threads whose memory is not properly released.
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'Try downloading and installing the 10.4.8 combo updater.' - it is rarely a good idea to install any updates to a currently dysfunctional operating system.
With respect to downloading and installing any Apple update, etc., consider downloading the respective installer(s) from '
Apple Downloads' (and
not using the 'Apple, Software Update' feature.
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Suggestion:
If your Mac boots and allows accesses to your '~/Library/Preferences/' folder ...
Follow bobw's advice and remove the 'com.apple.finder.plist' file (placing it on your 'Desktop' or in the Trash can) then relaunch 'Finder'. To do such - press and keep pressed the <option> key as you click on the 'Finder' icon, on the 'Dock', when the contextual menu appears - drag down (on the contextual menu) and select the 'Relaunch' menu item.
Next, instead of launching (opening, running) 'Disk Utility' - boot from the supplied Install Disk. Run 'Disk Utility' from the booted 'Install Disk', and do a 'Disk Repair' (at least twice) and then 'Repair Disk Permissions' (at least twice).
... otherwise ...
Follow bobw's advice of booting from the install disc and via it 'Terminal' application enter 'sudo rm ~/Library/Preferences/com.apple.finder.plist'
Next, run 'Disk Utility' from the booted 'Install Disk', and do a 'Disk Repair' (at least twice) and then 'Repair Disk Permissions' (at least twice).
Reboot your Mac, via its internal hard disk drive.
As time goes on - you will know if either process did / did not solve your problem(s).
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Other factors may be present - such as the quantity and / or size of your Mac's 'swapfiles' (accessible via 'Finder's 'Go, Go to Folder' menu item and entering '/var/vm/'); and, whether or not a '.log' file or files, due to a MacOS X hiccup, is / are corrupted - typically noted by being quite large in size (Log files can be located at '/var/log/' [use 'Finders' 'Go to Folder' menu item to access], '/Library/Logs/' and '~/Library/logs/').